Flexible Stellarator Could Give US an Edge Over China

A team of 24 physicists from leading US plasma research institutes has published a paper suggesting that if the United States wants to maintain its leadership in nuclear fusion technology, it should build a “flexible” stellarator that could eventually lead to a fusion power plant.

There is currently no planned or existing facility in the country where scientists could test their theories and concepts related to pilot fusion power plants.

“We therefore propose a new, flexible, mid-sized stellarator user device for confinement and diverter studies that will validate these theoretical advances and provide the physical foundations necessary for the fusion industry,” the authors of the study (white paper) said.

The study’s suggestions have enormous implications for the United States, given that China and Russia are actively developing their own nuclear fusion technologies.

Tokamaks vs. Stellarators

Nuclear fusion research is conducted using two types of devices: tokamaks and stellarators. These devices can confine hot plasma and achieve the conditions required for nuclear fusion reactions.

Scientists study these reactions to better understand nuclear fusion and the conditions necessary for a fusion power plant to operate.

Although both tokamaks and stellarators use magnetic fields to confine and manipulate plasma, they are not the same. Tokamaks are large, doughnut-shaped devices that use a toroidal magnetic field. They provide excellent performance when it comes to regulating plasma temperature.

Stellarators, on the other hand, have a complex structure involving a set of twisted coils that wrap around a toroidal chamber in a complex manner. They use twisted (helical) magnetic fields to confine the plasma.

Compared to tokamaks, stellarators are difficult to build and set up due to their complex geometry. However, they are more stable because, unlike tokamaks, they do not need a significant plasma current to generate a magnetic field.

Why build a stellarator when there are tokamaks?

The white paper’s lead author, Felix Parra Diaz, suggests that stellarators and tokamaks “are close relatives, sharing many common aspects. Physics discoveries that benefit one are usually of interest to the other.”

The United States has a number of highly efficient tokamaks, such as the DII-D and NSTX-U, but to fully leverage the technological advances these devices bring, the country also needs a flexible stellarator that can be adapted to a variety of experimental configurations.

“We need to create a convincing stellarator program in parallel with the tokamak program. Because the stellarator will prove to be a better path to the reactor if the theoretical predictions are confirmed and the new techniques and optimization strategies work as expected,” the study authors added.

They also propose a two-step approach to developing a flexible stellarator. The first step, called the “Exploration” phase, will focus on finding a magnetic configuration that will lead to minimal turbulence and optimized confinement.

In the second stage or “Operation” phase, the energy and heat management systems will undergo modernization. These changes will be implemented in accordance with the provisions of the first stage.

“If realized, these advances would lead to cost-effective stellarator designs with constraints comparable to tokamaks but without the fundamental challenges of interference and current drive,” the study authors added.

The flexible stellarator facility is not something that can be created overnight. According to researchers, it will take at least six to nine years to complete and launch.

However, once operational, such a center “would provide our national fusion research program with the ability to leverage expertise from diverse universities, national laboratories, and private industry, the flexibility to pursue a broad research program, and secure access to experiments,” the study authors note.

The study was published on arXiv.